WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT • The SCN1A and SCN2A genes encode α subunits of the neuronal voltage‐gated sodium channel, which are targets for various antiepileptic drugs such as carbamazepine, phenytoin, valproate and others. • Recent studies have demonstrated that various genetic variants of these channel genes play important role in the pathogenesis and therapy of epilepsy. WHAT THIS STUDY ADDS • This study demonstrates a significant association between the SCN1A c.3184 A→G; AG genotype and epilepsy. • However SCN2A c.56 G→A; allele ‘A’ was significantly associated with multiple drug resistance in epilepsy in north Indian population. AIMS To evaluate sodium channel genes as candidates for epilepsy susceptibility and their role in therapeutic efficacy, we screened coding single‐nucleotide polymorphism of SCN1A p. Thr 1067 Ala or c.3184 A→G (rs2298771) and SCN2A p.Arg19Lys or c.56 G→A (rs17183814) in north Indian epilepsy patients. METHODS The genotyping was performed in 160 control subjects and 336 patients with epilepsy, of whom 117 were drug resistant and 219 were drug responsive. Therapeutic drug monitoring for phenytoin, carbamazepine, phenobarbital and valproate was also performed in 20% of the patients to confirm compliance. RESULTS AG genotype of SCN1A 3184 A→G polymorphism was significantly higher and associated in epilepsy patients [P= 0.005; odds ratio (OR) 1.76, 95% confidence interval (CI) 1.19, 2.61], whereas A variant of SCN2A c.56 G→A was associated with multiple drug resistance in north Indian patients with epilepsy (P= 0.03; OR 1.62, 95% CI 1.03, 2.56). CONCLUSIONS Overall, results indicate a differential role of genetic polymorphisms of sodium channels SCN1A and SCN2A in epilepsy susceptibility and drug response.

In epilepsy, there is a tendency towards recurrent unprovoked seizures. Seizures result due to the excessive electrical misfiring in the brain between neurons and disturbance in neurotransmitter release. Several gene products affect the behavior of these neurons by regulating neurotransmission via several mechanisms. One such gene, Synapsin-2 (SYN2), involved in synaptogenesis is also reported to regulate the neurotransmitter release. We hypothesized that SYN2 gene and its polymorphisms could affect the process of epileptogenesis and therapeutic response in humans. In this hospital-based study, we enrolled 372 patients with epilepsy and 199 control subjects. We selected rs3773364 A>G polymorphism in SYN2 gene and analyzed its distribution in north Indian patients with epilepsy and control subjects. Genotyping was carried out by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method. According to the results obtained, SYN2 "AG" genotype frequency was significantly higher in patients with epilepsy versus control subjects in north Indian population (P = 0.02, OR = 1.55, 95% CI = 1.06-2.26). After subclassification, we observed higher frequency of AG genotype in idiopathic patients as compared to control subjects (P = 0.01, OR = 1.67, 95% CI = 1.08-2.56). There were no significant differences in genotypic (AG: OR = 0.80, P = 0.377; GG: P = 0.628, OR = 1.17) or allelic (P = 0.86, OR = 1.03) frequency distributions in patients with multiple drug resistance versus patients with drug-responsive epilepsy. Results from our study indicate the involvement of SYN2 gene polymorphism in conferring risk to epilepsy; however, the genetic variant does not seem to modulate drug-response in epilepsy pharmacotherapy.

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GABA (gamma-amino butyric acid) receptors have always been an inviting target in the etiology and treatment of epilepsy because of its role as a major inhibitory neurotransmitter in the brain. The aim of our study was to find out the possible role of single nucleotide polymorphisms (SNPs) present in GABRA1 IVS11+15 A>G (rs2279020) and GABRG2 588C>T (rs211037) genes in seizure susceptibility and pharmaco-resistance in northern Indian patients with epilepsy. A total of 395 epilepsy patients and 199 control subjects were enrolled for present study. The genotyping was done by PCR-RFLP methods. The GABRA1 IVS11+15 A>G polymorphism conferred high risk for epilepsy susceptibility at genotype 'AG' (P=0.004, OR=1.77, 95% CI=1.20-2.63), 'GG' (P=0.01, OR=1.80, 95% CI=1.15-2.80) and G allele level (P=0.001, OR=1.50, 95% CI=1.16-1.92). Moreover this polymorphism was also associated with multiple drug resistance in patients with epilepsy for homozygous variant 'GG' genotype (P=0.031, OR=1.84, 95% CI=1.05-3.23) and G allele (P=0.020, OR=1.43, 95% CI=1.05-1.95). However GABRG2 588C>T polymorphism was not found to be associated either with epilepsy susceptibility or with drug resistance. Overall results indicate differential role of different subunits of GABA(A) receptor subtypes in epilepsy susceptibility and pharmacotherapy.